Build: fix a rule in the opam file (the remove script is in etc/lutin, not etc/Lutin)

2 jobs for 2.70.4 in 8 minutes and 47 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #92453
build

00:04:43

 
  Test
passed #92454
test_opam_test

00:04:03